Capturing images of light or other (including radiological) signals emitted from specimens during a chemical reaction has been used to determine the components of a specimen based on where spatially separated bands or regions of light are emitted from the specimen. Certain components of a specimen may emit light in brighter bands of light requiring shorter exposure times for image capture while other constituents may emit light in dimmer bands requiring longer exposure times. Problems can arise when “read noise” occurs during image capture and distorts the captured image, particularly for specimen components that emit light in weakly emitting bands.
In order to overcome read noise limitations for weak samples, it is common to integrate or collect the charge over a long exposure of the CCD or CMOS. The long exposures do not allow the measurement system to measure the signal in continuous-like fashion. In other works, one could take many shorter images, but the system would not be very sensitive because read noise would be introduced with each short exposure. If you sum the short exposure, this helps reduce the read noise some but it is still not as sensitive as conducting one long exposure using a conventional image sensor. In this case of image summing, the read noise is known to increase in captured images as the square root of the number of exposures.
Many trained artisans in the field have therefore struggled with solving the problem of monitoring weak chemical reactions in a continuous-like manner while maintaining high sensitivity. As discuss below, there a several key advantages to method that would allow fast monitoring of chemical reactions while not compromising sensitivity.